Various tests have been developed to ensure that concrete used in particular applications satisfies specifications. One of these is a compression test for testing concrete cylinders. Initially, the tests were performed by capping freshly molding concrete cylinders with materials such as sulfur mortar. This provides a smooth, hard surface which fills any imperfections which normally occur when making the concrete cylinder. These procedures require considerable preparation time.
More recently, unbonded capping systems have been developed. A typical unbonded capping system comprises a pair of retaining cups and a pair of compression pads. Each retaining cup retains one of the compression pads and fits over one end of the concrete cylinder. This assembly is then placed between the platens of a compression testing apparatus which compresses the sample to failure. The compression pad, which is made of a tough elastomeric material, flows into irregularities in the concrete cylinder and distributes the test load uniformly without creating air pockets to assure consistent breaks. The tests for using unbonded caps are specified in ASTM Standard C1231 and AASHTO Standard T22. Under both standards the compression pad has a smaller outer diameter than an inner diameter of the retaining cup. As a result, there is a circumferential space between the compression pad and the retaining cup. As a result, the compression pads frequently fall out of the retaining cups during test preparation.
The present invention is directed to further improvements in concrete cylinder compression testing.